The present invention is generally concerned with mobile radiocommunication systems.
The present invention is more particularly concerned with power control used in such systems to improve performances (in terms of quality of service, of capacity, . . .etc.).
The present invention is in particular applicable to mobile radiocommunication systems of CDMA (xe2x80x9cCode Division Multiple Accessxe2x80x9d) type. In particular, the present invention is applicable to UMTS (xe2x80x9cUniversal Mobile Telecommunication Systemsxe2x80x9d).
One type of power control which is used in CDMA systems is the so-called closed-loop power control.
The closed loop generally runs on a fast basis in order to adjust the transmission quality (generally represented by the SIR, or xe2x80x9cSignal-to-Interference Ratioxe2x80x9d) around a transmission quality target value (generally a SIRtarget value), by sending appropriate power control commands back to the transmitter. The closed loop thus sends an xe2x80x9cupxe2x80x9d power control command back to the transmitter when the estimated SIR is below the SIRtarget value, or a xe2x80x9cdownxe2x80x9d power control command otherwise.
The SIRtarget value is generally adjusted by a so-called outer loop. The outer loop generally runs on a slower basis in order to adjust the quality of service (generally represented by the BER, or xe2x80x9cBit Error Ratexe2x80x9d, or the FER, or xe2x80x9cFrame Error Ratexe2x80x9d) around a quality of service target value (generally a BER or FER target value).
The outer loop thus increases the SIRtarget value when an estimated BER or FER is above a BER or FER target value, or reduces it otherwise.
Such an implementation may lead to such situations where the SIRtarget value is needlessly increased, therefore needlessly increasing the interference level in the system.
This may in particular be the case under such conditions as when the transmitter has already reached its maximum transmit power, or when the system has become overloaded. In such a case the SIRtarget value is uselessly increased, while this cannot result in any quality improvement. This may not be considered as a drawback in itself, as long as such conditions apply, but the SIRtarget value may therefore reach a too high value, and, when such conditions no longer apply, this will result in setting the transmit power at a level higher than necessary, therefore needlessly increasing the interference level in the system, until the algorithm reaches a correct value again.
The outer loop is usually implemented at the receiver side in order to reduce adaptation delays between quality measurements and SIRtarget setting. However, the receiver may not have means to know why the quality of service cannot be maintained with the current SIRtarget value, and, as indicated above, may try to increase if, even though the current SIRtarget value cannot be reached due to network overload for instance.
Therefore there is a need to provide a power control method avoiding such drawbacks.
An object of the present invention is therefore a method for improving performances of a mobile radiocommunication system using a power control loop which controls power according to a transmission quality target value, and an adjustment process for adjusting said transmission quality target value, a method wherein said adjustment process is limited, based on the thus controlled power reaching a maximum value.
According to another object of this invention, said limitation of said adjustment process includes not increasing said transmission quality target value if the thus controlled power has reached a maximum value.
According to another object of this invention, said mobile radiocommunication system is of CDMA type.
According to another object of this invention, said adjustment process is an outer loop which adjusts a quality of service around a quality of service target value.
According to another object of this invention, said power control is performed in a downlink transmission direction of said mobile radiocommunication system, using a downlink power control loop and a downlink adjustment process, and said downlink adjustment process is limited, based on the thus controlled power reaching a maximum value.
According to another object of this invention, said power control is performed in an uplink transmission direction of said mobile radiocommunication system, using an uplink power control loop and an uplink adjustment process, and said uplink adjustment process is limited, based on the thus controlled power reaching a maximum value.
The present invention also has for its object a mobile radiocommunication system for performing such a method, said mobile radiocommunication system being of the type comprising at least one mobile station in turn comprising means for performing said downlink adjustment process, and a mobile radiocommunication network in turn comprising at least one base station and at least one base station controller, and said system comprising means for limiting said downlink adjustment process, based on the controlled power of a base station transmitter reaching a maximum value.
According to another object of this invention, said limitation is performed for all mobile stations connected to said base station.
According to another object of this invention, said limitation is performed only for those mobile stations for which said base station transmitter cannot transmit the required power.
According to another object of this invention, said limitation is not performed for those mobile stations connected at the same time to other base stations, when the transmitter power of at least one of these other base stations does not reach a maximum value.
According to another object of this invention, a base station of such a system comprises:
means for transmitting to a base station controller, information as to a base station transmitter reaching a maximum power value.
According to another object of this invention, a base station controller of such a mobile radiocommunication system comprises:
means for receiving such information from a base station, and for providing a corresponding limitation information,
means for transmitting such limitation information to at least one mobile station.
According to another object of this invention, a base station controller of such a mobile radiocommunication system comprises:
means for receiving power measurement reports from a base station, and for providing a limitation information, based on an information as to a base station transmitter reaching a maximum power value, deduced from such power measurement reports,
means for transmitting such a limitation information to at least one mobile station.
According to another object of this invention, a mobile station of such a system comprises:
means for receiving such a limitation information from a base station controller,
means for limiting said downlink adjustment process, based on such a limitation information.
The present invention also has for its object a mobile rodiocommunication system for performing such a method, said mobile rodiocommunication system being of the type comprising at least one mobile station and a mobile rodiocommunication network in turn comprising at least one base station and at least one base station controller, in turn comprising means for performing said uplink adjustment process, and said system comprising means for limiting said uplink adjustment process, based on the controlled power of a mobile station transmitter reaching a maximum value.
According to another object of this invention, a mobile station of such a such a system comprises:
means for transmitting to a base station controller information as to a mobile station transmitter reaching a maximum power value
According to another object of this invention, a base station controller of such a system, comprises:
means for receiving such information from a mobile station,
means for limiting said uplink adjustment process, based on such an information.
According to another object of this invention, a base station controller of such a system, comprises:
means for receiving power measurement reports,
means for limiting said uplink adjustment process, based on an information as to a mobile station transmitter reaching a maximum power value, deduced from such power measurement reports.